Air-speed indicator



Allg- 7, 1951 J. E. BEvlNs AIRSPEED INDICATOR 2 Sheets-Sheet l OriginalFiled June '7, 1943 INVENTOR- J. E. BEVINS AIRSPEED INDICATOR Aug. 7,1951 2 Sheets-Sheet 2 Original Filed June 7, 1943 3 is providedwithtwolaligned lugs 3l and 38 which form apivoted i'supportfor sidfrockerbracket between the screw pins 39 and 40 threaded in a frame 4I fixed inthe casing l0. Pins 39 and 40, and pin 34 of yoke 35 are in alignmentwhen the instrument is not in use.

Rocker bracket lug 31 has associated therewith a hair spring 31a securedatthe outer end to pin 4la and lug 38 has clamped thereto an elongatedsplit lug 43 clamped thereto by screw 44. Split lug 43 is apertured atAthe opposite end (see Figure 4) to receive elongated bar 45. Bar 45 isadjustably secured in the split lug aperture by set screw 46, so that anend protrudes therefrom at 41 to which is pivfted link 48. .liinkit'isadjustablywseeured to inwardly extending lug 49 of diaphragm 50 by setscrew 5l.. and any back-lash in link 48 is taken out by hair spring 31a,see Figure 3. Y y d Secured to oscillator bar 33 is a segment gear 52 sopositioned as4 to Ymesh with a pinion 53 of indicator .spindle 24, thatcarries indicator handl. g A The above described linkage. is generallyref erred to herein as any suitable diierential linkage.

As shown in Figures 1 and 2, compensator diaphragm 50 is connected toV acapillary tube 54, connected in turn to a bulb or coil 55, which issubject to the temperature that is to be measured. The coil or bulb 55is completely lled with gas adsorption medium, such as activatedcocoanut charcoal granules 56, before it is soldered to the capillarytubing 54. The system is then completely evacuatedvwith the bulb 55 atapproximately 150 C. It is then ycharged with any suitable dry gas, ascarbon dioxide (CO2).

e During the lling operation, bulb 55 is gradually cooled to the lowesttemperature that it is expected to encounter in service, while theiilling gas is still connected to the system. The bulb 55 is next sealedand the gas is in contact with the diaphragm 50 and the activatedcocoanut char- Icoal in bulb 55 for the purpose referred to under thefollowing heading.` Y

Operation Assuming the entire deviceto be installed in an aircraft, theproximate cause of compensation for varying air densities is thereaction of charcoal contained in bulb` 55 with the -CO K2 gas. As thecharcoal is cooled, it adsorbs the gas and causes a partial vacuum inthe system. When it Ijheated, the opposite eifectis present andA causesa pressure to expandthe diaphragm 5th This` expansion and contraction ofthe sensitive element 50 is transmitted through the diierential linkaget o give correct compensation of a true airspeed indicator. e e Y Ashereinbefore indicated the. pins 39 and 40, and pin 34 are in alignment`when the instrument is not in use. The expansions and contractions o fthe diaphragml dueto the varying pilot pressures will be transmittedfbylink 29 to the link 30 by reason of its connection therewith by the pin34. Y The motion ofthe link 29 in moving the link 30, will cause theyoke `3,5 to rotate about its pivot pin-36a inthe rocker bracket 36. Themotion thus transmittedwill rotate the segment gear 52 to rotate spindle24. Pointer I6 will move over an airspeed dial (not shown) to indicateairspeed. A l Y y Expansion and contraction uof the diaphragm 50 due tochanges in temperature-will move the link 4,8` causing the rockerbracket .,36 to rotate about its pivot on pins 394|l.f1?he rotation ofthe bracket 36 will cause tliepin 35a thereinto move in an arc about theaxis determined by the screw pins 39, 40. With the diaphragm 25unaffected by Pitot pressures, no motion due to the expansion or'contraction of diaphragm 50 will be transmitted by link 30 to thespindle 24. The point of pivot of link 30 (and 29) is not varied. Thusthe arrangement described will not ailect the "zero position or pointerI6.

The arcuate displacement of pin 36a will vary the eiective lengths oflinks 29 and 30 due to the changein the relative position of their pointof pivot. The rotation ofsegment gear 52 by the links 29, 30 is thuscompensated for air temperature and density. VThepointer. |6Awill. thus,beY rotated to indicate true airspeedin contradistince tion toindicated airspeed heretofore had.,

If we assumethe aircraft to be travelling at a constant velocity withthe pivot point 34 at a position slightly above the position shown inFigs. 3 and 4 and an increase in altitude takes place with anaccompanying decrease in temperature, the diaphragm 50 will tendtocontract due to the absorption of CO2 gas. Under, these conditions,however, the pressure of the air surrounding the diaphragm 50 willdecrease and tend to expand the diaphragm. The net result will be theexpansion of the diaphragm 50 inasmuch as the effect on the diaphragm ofthe air pressure is greater than the effect of the instant temperaturein varying the pressure of CO2 in the-diaphragm. This result is readilyapparent when itis considered that the amount of effective change inpressure with a change in altitude is greater than the amount ofeffective change in'temperature with the same change in altitude.Diaphragm 50 is so calibrated that with .changes in altitude theeffective force which predominates is that due` to air pressure, butrtemperature, compensation is added thereto in order to provide for atrue air-f speed indication.

The expansion of the diaphragm upon an increase in altitude will shiftthe link 48 to the left (Figs. 3 and 4) to rotate the rocker bracket 36clockwise about its pivots 39, 40 (34) The pivot; 36a of links 29 and 30in yoke 35. will be rotated clockwise or moved downwardly and slightlyto the left. The pivot point 34 of links 29, 30 will thus be rotatedclockwise. to increase the obtuse angle formed by the links. Themovement of pivot 34 will push link 3U upwardly Ato rotate segment gear52 in a clockwisedirection in Fig. 3 to increase the indication toapproach true airspeed of the craft. This will. give the trueairspeed ofthe craft becausetheair Ofdecreased. density which'aetuates diaphragm 25and links 29,730 tends todecrease the4 indication below its true value.With the aid of the compensator diav phragm 50 the driven link 30 will`be `urged in the directionmentioned to offset the ,decreased pressureon the air speed diaphragm 25 due to the increase in altitude.

. A decrease in altitude andan increasey in air temperature with aconsequentincrease in pressure and density at both diaphragmsl and 50,will contract the last-mentioneddiaphragm and, shift link- 48 `to theright to decrease the obtuse angle formed by links 29, 30 to decreasethe reading of the indicator. In this manner, increased, pressure in thediaphragm 25 will; beovercome by the movement of link V48 to the rightto urge linkv 30 and gear 52 in a counterclockwise direction to decreasethe 'reading .of hthe .iridiatory-`r Thus, for

asdaaov sure with the resultant changes in density, the indicator willeffect a reading of the true airspeed of the air-craft.

The characteristics of the system can be lcon-- trolled by making alarger or smaller bulb and putting in varying amounts of activatedcocoanut charcoal.

Any other type activated carbon can be used to fill such a system, butfcocoanut charcoal is satisfactory as it is most active for gasadsorption.

It will thus be seen that there is provided a true airspeed indicator inwhich the several objects of this invention are achieved, and which iswell adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention andas various changes might be made in the embodiment set forth, it is tobe understood that all matters herein set forth, or shown in theaccompanying drawings are to be interpreted as illustrative and not in alimiting sense.

y What I claim is:

1. An airspeed indicator, comprising a pressure actuated member adaptedto be actuated by the static and dynamic air pressures as delivered by aPitot tube, an indicator for said member, means for driving saidindicator by the expansion and contraction of said member to indicateairspeed; a temperature responsive element, a second pressure actuatedmember subject to static air pressure, means for interconnecting theinteriors of said element and of said second member, a gaseous medium inthe interconnected interiors and a gas-occluding medium in said elementadapted to adsorb and expel said gaseous medium due to temperaturechanges for expanding and contracting said second pressure member; andmeans operative by the expansion and contraction of said second memberto vary said indicator drive means in accordance with the changingtemperature and static air pressure to indicate true airspeed.

2. A true airspeed indicator comprising a differential pressureresponsive member actuated by static and impact pressures, an indicatorfor said pressure responsive member, variable means for driving saidindicator by the expansion and contraction of said member for indicatingairspeed, a temperature responsive element containing a gas occludingmedium and a gaseous medium, and a container having a movable walloperated by the gas pressure, said container being also subjected tostatic pressure and said wall being connected to said driving means,said gas operated container communicating with said temperatureresponsive element and adapted to be actuated by the static pressure andthe pressure changes in the gaseous medium due to the varying absolutetemperature surrounding said element to vary said driving means of saidindicator in accordance with varying air densities to effect anindication of true airspeed.

3. A true airspeed indicator comprising a casing, means comprising ayieldable wall movably mounted within said casing and exposed on oneside thereof to static pressure communicated from the exterior of thecasing and on the opposite side thereof to dynamic pressure communicatedfrom the exterior of the casing, means comprising a pointer connectedfor operation by said wall, temperature and pressure compensating meansconnected to modify operation of the pointer by the wall, saidlast-named means Comprising a closed expansible and contractiblecontainer mounted in said casing and exposed to static pressure on theoutside thereof, said container being provided with a gas therein, andmeans outside of said casing responsive to temperature changes andconnected with the inside of said container for changing the gaspressure therein.

4. A true airspeed indicator comprising a casing, means comprising ayieldablewall movably mounted within said casing and exposed on one sidethereof to static pressure communicated from the exterior of the casingand on the opposite side thereof to dynamic pressure communicated fromthe exterior of the casing, means comprising a pointer connected foroperation by said wall, temperature and pressure compensating meansconnected to modify operation of the pointer by the wall, saidlast-named means comprising a closed expansible and contractiblecontainer mounted in said casing and exposed to static pressure on theoutside thereof, and means responsive to temperature changes including atemperature responsive element located outside of said casing and havinga gas occluding medium and a gaseous medium therein communicating withthe container, whereby changes in static pressures and in ambienttemperatures exterior of said temperature responsive element vary thegas pressure in said container to modify the operation of the pointer.

5. A true airspeed indicator comprising a casing, means comprising ayieldable wall movably mounted Within said casing and exposed on oneside thereof to static pressure communicated from the exterior of thecasing and on the opposite side thereof to dynamic pressure communicatedfrom the exterior of the casing, means comprising a pointer connectedfor operation by said wall, a helically formed temperature responsiveelement located externally of the casing and containing a gaseous mediumand a gas occluding medium thereinan expansible and contractiblecontainer mounted within the casing subject to static pressure andcommunicating with said temperature responsive element, said containerbeing expanded and contracted by said mediums upon changes intemperature of the air about said element, and means drivablyinterconnecting the pointer and said container for varying the movementof the pointer.

JAMES E. BEVINS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,159,893 Browne et a1 Nov. 9,1915 1,272,554 Steenbierg July 16, 1918 1,489,463 Sherrin Apr. 8, 19241,722,619 Ziegler July 30, 1929 1,839,077 Adams Dec. 29, 1931 2,050,965DeGiers Aug, 11, 1936 2,221,633 Dasher Nov. 12, 1940y 2,251,498 SchweinAug. 5, 1941 2,302,713 Paulin Nov. 24, 1942 2,318,153 Gilson May 4, 19432,379,874 Bean July 10, 1945 FOREIGN PATENTS Number Country Date 374,730Germany Apr. 27, 1923

